IPTABLES

To block specific port number such tcp port # 5050, enter:

iptables -A OUTPUT -p tcp --dport 5050 -j DROP

To block tcp port # 5050 for an IP address 192.168.1.2 only, enter:

iptables -A OUTPUT -p tcp -d 192.168.1.2 --dport 5050 -j DROP

Show NAT rules

iptables -nvL -t nat